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SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
Grafoil® rings
– die-moulded
expanded graphite
Material description:
Properties:
Grafoil® is made of 100% natural graphite,
which is treated with acids and high temperature according to a specially developed
process. The result is expanded graphite,
which after calendering, becomes a soft and
flexible foil that is used for manufacturing
gaskets. Grafoil® contains no binders or
other additives, but is a pure carbon product
in the form of graphite.
Permanent elasticity, does not harden at
high temperature, does not dry, does not
shrink.
Applications:
Broad medium resistance range.
Thanks to its unique properties, Grafoil®
is ideal as a packing material for valves,
pumps and agitators.
Can be used for more or less all media such
as water, steam, acids, alkalis, petroleum
products, solvents and gases, but not for
strongly oxidising acids such as sulphuric
acid and nitric acid in combination with high
temperature plus chromium solutions and
hot permanganate. We do not recommend
graphite in combination with sea water and
stainless steel.
Abrasive media and equipment with large
shaft runout should be avoided.
Standard types
Stable volume, practically no compression
set in heat.
Fireproof, meets requirements as per API 607.
Self-lubricating, low friction.
Extremely good thermal conductivity.
Very good sealing capability, hence low
emissions.
BAM-approved for oxygen and liquid oxygen*.
Good resistance to radioactive media.
Unlimited service life results in unsurpassed
economy.
Extremely low chloride content minimises
the risk of corrosion of stainless steel.
No corrosion inhibitor is needed.
Technical data:
Temperature limit:
-200°C to +550°C in air
max. +2500°C in nonoxidising atmosphere
max. +200°C in oxygen
pH range:
0-14
Graphite content: min. 98.0% industrial quality
min. 99.5% nuclear power quality
Max. content of leachable chlorides:
Max. sulphur content:
Max. surface speed:
Square or
rectangular cross-section
Cover plate seal with
45° internal chamfer
Cover plate seal with
45° external chamfer
Special types of cover plate seals with stainless steel caps
Cover plate seal with
internal radius
50 ppm
550 ppm
25 m/s
Max. pressure:
60 bar in pumps
700 bar in valves
Purity:
The Swedish nuclear power industry,
which has the most stringent requirements,
normally accepts max. 50 ppm leachable
chlorides. We can supply Grafoil® with a
certified max. 50 ppm, but the content in
Grafoil® is normally approx. 10 ppm.
Documented max. chloride content, as well
as other quality documents can be supplied
if requested.
*) If BAM certification is required for this product,
this must be specified at the time of ordering.
Type SF
Type SR
Type ST
The stated limit values apply under favourable conditions.
Do not utilise more than one maximum value at a time.
If in doubt please contact us, we will be happy to offer advice.
SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
Manufacturing:
Recommended densities for
die-moulded Grafoil rings:
Rings are manufactured with a square or
rectangular cross-section, or with a chamfer (for
valve covers) or other special cross-section.
The rings can be pressed to different densities
to specification from 1.3 to 1.8 g/cm3. All rings
can be supplied endless or split, with straight or
diagonal cut. Cut rings can be threaded onto a
shaft even if the shaft end is not accessible.
For normal use in valves:
Die-moulded graphite ring with stainless steel antiextrusion caps.
1.8 g/cm3
For valve cover seals:
1.8 g/cm3
For rotating shafts:
1.4 g/cm3
If you wish to manufacture Grafoil® sealing
rings yourself, we can offer the Grafoil® Ribbon Pack, expanded graphite in the form
of corrugated ribbon supplied in the following standard dimensions:
Dimensions:
Standard tolerances for Grafoil rings:
Inner diameter
Ø < 50 mm
Ø 50-150 mm
Ø 150-300 mm
Ø > 300 mm
+0.3/-0+0.5/-0+0.7/-0+1.0/-0
Outer diameter
Ø < 50 mm
Ø 50-150 mm
Ø 150-300 mm
Ø > 300 mm
+0/-0.3+0/-0.5+0/-0.7+0/-1.0
Ring height
Dimensions Metres
mm
per box
Part
number
12.5 x 0.5
19 x 0.5
25 x 0.5
30
30
30
362212
362219
362225
38 x 0.5
50 x 0.5
30
30
362238
362251
We stock the most common dimensions for
valves, pumps and sootblowers.
Alternative versions of packing sets:
We can offer complete sets in versions suitable for special requirements. A few examples
are shown below:
Std version with
scraper end rings
and extra
diffusion barrier of
soft gaskets.
Die-moulded Grafoil rings
±5%
Specmaseal Type S
std version with scraper
end rings made of die
moulded carbon fibre
braided packing,
see page 24.
For valves with large clearances:
Grafoil® Ribbon Pack
– ribbon material:
For static applications with large clearance
and/or high pressure, e.g. for valve covers
and heat exchangers, die-moulded rings
fitted with a stainless steel cap can be
supplied to prevent the risk of extrusion.
These rings normally have a rectangular
cross section or a 45° chamfer.
Std version with
filler bushing.
1.4-1.5 g/cm3
Specmaseal Type F with
bevelled rings and scraper
end rings for improved
transverse expansion,
see page 24.
Grafoil® is a registered trademark of
GrafTech International Holdings Inc.
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SPECMA SEALS HANDBOOK
S T U F F I N G B OX PA C K I N G S
Grafoil® rings – Ribbon Pack installation instructions
For valves:
1. Clean the stem and stuffing box thoroughly. Replace damaged mechanical
parts. Lubricate the stem with Grafex®
GTL graphite paste and carefully rub in
the graphite. Wipe off excess grease.
2. Select a suitable ribbon width.
3. Wind Ribbon Pack around the stem until
the box is full.
4. Push the packing material down into the
stuffing box.
5. Use a split mounting sleeve and push
the first ring down to the bottom of the
box.
6. The clearance between the mounting
sleeve and the stem or box wall must not
exceed 0.25-0.30 mm.
11.Do not mix Grafoil® Ribbon Pack with
stuffing box packing braids of materials
other than carbon fibre and expanded
graphite.
12.For final adjustment of the gland:
loosen it and check that the stem can be
rotated. Then tighten the gland gradually
until the valve does not leak under pressure. The gland does not normally need
readjustment.
Selection of Ribbon Pack width
If packing
space width is:
Use
Ribbon Pack
width:
Up to 6 mm
12.5 mm
6 mm - 10 mm
19.0 mm
10 mm - 13 mm
25.0 mm
13 mm and above 38.0 mm
Note: In certain cases, the access between the upper edge of the stuffing box and the lower
part of the gland can be limited, for which reason a narrower ribbon than recommended must
be used. When ordering ready made die-moulded rings, state the required density or area of
use.
7. Using the gland and the mounting sleeve
to compress the first ring; at least 50
MPa pressure is recommended, which
gives approx. 50% compression and a
density of approx. 1.6 g/cm3.
8. Loosen the gland, remove the mounting
sleeve and check that the stem can be
rotated.
9. The following rings are installed and
compressed one at a time, as described
in sections 3-6.
10.We do not recommend installing more
than 4 to 6 rings. If the stuffing box is
very deep, a filler bushing of carbon or
suitable metal should be fitted in the
bottom.
For pumps:
1. Follow the installation instructions for
valves in sections 1-11, but the rings
must be compressed to max. 25 MPa
(250 bar) pressure, giving a density of
approx. 1.4 g/cm3.
2. Once all the rings have been installed,
start the pump. Leave the gland
tightened only finger-tight to avoid
overheating the shaft during the
running-in period.
3. If the media so allows, a certain amount
of leakage simplifies running in. Adjust
the gland nuts one flat at a time, until
the leakage is reduced to 20-60 drops/
minute, depending on the application.
4. The stuffing box does not need to be
totally emptied for packing replacement
with clean media. If necessary fill up
with a Ribbon Pack ring.
Fig. 1.
Ribbon Pack is wound
around the stem.
Fig. 2.
Use a split mounting sleeve
for compression.
Note: If the diametrical clearance between the
stem and box bottom exceeds 0.5 mm or if
the media contains abrasive particles, a ring
of braided carbon fibre packing material (e.g.
Garlock 98®) should be placed in the bottom.
Installation instructions for readycut die-moulded rings:
1. If the stuffing box is unnecessarily
deep (more than 5-6 rings) or if the
clearance between the stem and the
box bottom is too large (more than 0.5
mm diametrically), start by installing
a suitable filler bushing of carbon or
suitable metal, or shims.
2. Install the first Grafoil® ring separately
and push down to the box bottom using
a mounting sleeve (possibly split).
This sleeve shall have max. 0.6 mm
diametrical clearance toward the stem
and box walls. If a free shaft or stem
end is not available, you may cut the
The stated limit values apply under favourable conditions.
Do not utilise more than one maximum value at a time.
If in doubt please contact us, we will be happy to offer advice.
Fig. 3.
Each ring is compressed
individually.
die-moulded ring, either straight or at an
angle. Open the ring carefully axially and
fit it over the shaft or stem. Make sure
that the rings are installed with the cuts
displaced by 120° to each other.
3. Compress the ring with the mounting
sleeve, gland nuts and gland. Use
normal ring spanners and tighten as
hard as you can.
4. Repeat the process for the following
rings, one or max. two at a time.
5. Then follow the instructions according to
sections 10-12 for valves and 2-4 for pumps.
Note: Only by compressing the rings one at
a time with the mounting sleeve can you be
sure that the first ring (bottom ring) seals.
Note: The stuffing must be tightened as
hard as possible and then loosened and
thereafter be adjusted.